This invention relates to apparatus in an electrostatographic copier or printer for developing electrostatic images with toner, and more particularly to a mechanism in a space restricted development apparatus for automatically and gradually lifting a toner container in order to maintain contact between toner in the container and means, including a replenishment roller, for transferring the toner to the electrostatic images.
In electrostatographic copiers and printers, electrostatic images, on an insulated image bearing member, such as a photoconductor, are developed, that is, made visible with toner particles. Such development can be carried out with a development apparatus that typically includes a development roller, a toner replenishment roller, and a container for holding the toner particles. The development roller, which rotates about a fixed axis, and spaced from the image bearing member, functions to carry and bring toner particles into transfer contact with electrostatic images on the image bearing member. The toner particles which are precharged, triboelectrically, for example, are supplied to the development roller by the toner replenishment roller. The toner replenishment roller rotates about a fixed axis, and is in contact with the development roller. -n addition, the replenishment roller must also rotate in contact with the toner particles being held in the container or sump portion of the development apparatus.
As disclosed, for example, in U.S. Pat. No. 4,353,637, issued Oct. 12, 1982 in the name of Parker, the transfer in electrostatographic copiers and printers, of toner particles from a toner container to electrostatic images on an image bearing member, over time, depletes the quantity of toner particles available in the container. Such depletion eventually will drop the level of toner particles within the container below and out of contact with the means for transferring the toner to electrostatic images. As also disclosed, for example, in this patent, and in U.S. Pat. No. 4,417,802, issued Nov. 29, 1983 in the name of Forbes, mechanisms have therefore been provided for vertically lifting the toner container in order to retain contact between the dropping level of depleting toner in the container and such transfer means. As also disclosed, it is well known to use bellows, pressurized air or vertically acting spring mechanisms, for example, for lifting the toner container in order to achieve such contact.
However, bellows and pressurized air mechanisms are bulky, and at best expensive. In addition, because of design limitations in the relationship between the free length and the available deflection of springs, vertical spring mechanisms often require a lot of vertical space to operate, and therefore may not be able to function effectively within a height restricted environment. Furthermore, vertical springs usually are susceptible to buckling failure.